Using GaN HEMTs for high performance in USB-C designs

GaN HEMTs operate at the high switching frequencies need for high power density USB-C adapter and charger designs. Luo Junyang, technical marketing at Infineon Technologies, discusses alternative approaches to implementing common topologies found in USB-C power delivery (PD) designs.

Modern USB-PD adapters and chargers (including those with extended power range) are required to deliver exceptional performance in the smallest possible form factors. There are a range of topologies commonly used: active clamp flyback, hybrid flyback, as well as PFC and hybrid for extended power range. But what are the pros and cons of implementing them using discrete devices versus fully integrated GaN HEMTs? And what might be the benefits from using integrated switching controllers, where appropriate to a topology?

Active clamp flyback - Discrete
We’ll start with one of the most popular topologies: the active clamp flyback (ACF) converter which enables zero voltage switching (ZVS) for power switches. The topology (Figure 1) is suitable for higher frequency operation than a quasi-resonant flyback due to the ZVS operation and complete recovery of the energy in transformer leakage inductance dissipated in the flyback resistor-capacitor-diode (RCD) clamp. Clamping the primary-switch voltage through the clamp capacitor (combined with ZVS) means the ACF topology provides good electromagnetic interference (EMI) performance.